1. Field of the Invention
The present invention relates to an imaging apparatus and a control method thereof that enable image shake in a rotation direction whose rotation axis is the optical axis of an imaging optical system and that is produced by shake of the imaging apparatus to be corrected.
2. Description of the Related Art
In recent years, there have been imaging apparatus such as digital cameras and digital video cameras that are capable of optically correcting vibrations (camera shake) conveyed from the user's hand in a direction perpendicular to the optical axis of an imaging optical system, by driving the image sensor or a correction lens provided in the imaging optical system. On the other hand, since it is unrealistic from a production cost viewpoint, to provide the image sensor with a rotation mechanism in order to correct the rotary component of an image whose rotation axis is the optical axis of an imaging optical system produced by camera shake, the problem of correcting the rotary component is solved by image processing that involves rotating the image in the opposite direction to the detected rotation around the optical axis.
For example, in the case where triaxial movement directions are defined as shown in FIG. 2 relative to the positional relation of the imaging optical system and the image sensor, the optical axis direction will be the Z axis, the Y axis will be the upward direction of the imaging optical system, and the X axis will be orthogonal to the Y and Z axes. At this time, the rotary component of shake of the imaging apparatus is detected separately as three components consisting of a pitch component, which is rotation around the X axis, a yaw component, which is rotation around the Y axis, and a roll component, which is rotation around the Z axis. Since the rotation of the pitch and yaw components can be regarded as a translational movement in the X and Y axial directions, camera shake can be reduced by driving the imaging optical system so as to reduce movement of the image formed on the image sensor. In contrast, in order to correct the rotation of the roll component (rotary shake), which is rotation around the optical axis of the imaging optical system, correction is performed by an image processing circuit provided in the imaging apparatus, for example.
In the case where rotary shake at an angle θ in the counterclockwise direction is detected as the rotation of the roll component such as shown in FIG. 3A, a captured image 300 output from the image sensor is rotated such that the vertical direction of the object image rotates by the angle θ in the clockwise direction. Thus, by clipping an area 301 that has been rotated by the angle θ in the opposite direction to the direction of the detected rotary shake, that is, in the clockwise direction, an image 305 corrected for rotary shake can be generated. However, correcting rotary shake results in information (shaded areas in FIG. 3A) on an angle of view that is not included in the captured image 300 constituting the imaging range being included in the image 305 corrected for rotary shake. Thus, when outputting an image corrected for rotary shake that has the same pixel count as the captured image, it is necessary to clip the maximum area having the same aspect ratio as the captured image from an area of the image 305 that does not include the shaded areas, and apply electronic zoom to the clipped area. In contrast, Japanese Patent Laid-Open No. 2009-124314 discloses a method of correcting rotary shake, by clipping a rectangular area rotated by the rotation amount in the opposite direction to the rotary shake, so as to fit within the area of the captured image.
There are also imaging optical systems that have distortion aberration due to the influence of the curvature of the respective lenses, and when imaging is performed using such an imaging optical system, barrel distortion aberration may occur in which the image formed on the image sensor is distorted toward the center particularly at the wide-angle side. Heretofore, in order to correct barrel distortion aberration, a distortion aberration-corrected image 315 having the same pixel count as the captured image can be obtained, by clipping a barrel-shaped area 311 from the captured image 300 and performing distortion aberration correction on the clipped area as shown in FIG. 3B. Japanese Patent Laid-Open No. 2007-293457 discloses a technique for clipping and outputting a desired range from the area of an object image, out of an image obtained by correcting rotary shake after performing distortion aberration correction, in an imaging apparatus having an imaging optical system in which distortion aberration changes between being barrel-shaped and pincushion-shaped depending on the zoom ratio.
However, when performing distortion aberration correction, information (shaded portion in FIG. 3B) on the areas of the four corners that cannot be referenced from the image 315 to which distortion aberration correction has been applied may be eliminated, since the barrel-shaped area is clipped from the captured image 300 and expanded as shown in FIG. 3B. Thus, with methods that involve clipping an image corrected for rotary shake from an image to which distortion aberration correction has been applied, such as Japanese Patent Laid-Open Nos. 2009-124314 and 2007-293457, there is possibly information on the captured angle of view constituting the captured image that cannot be used effectively. That is, since information on the four corners is eliminated from the captured image output by the image sensor due to distortion aberration correction, and information is further extracted when rotary shake correction is performed, an image corrected for rotary shake having a narrower angle of view than the captured angle of view may be obtained.